   (tuc/draw-normal 13750 2150))
 
 (defn typical-stage-length
-  ([] (let [length-unit (rand-nth [:ft :m])]
-        [length-unit (typical-stage-length length-unit)]))
+  ([] (typical-stage-length (rand-length-unit)))
   ([length-unit]
    (condp = length-unit
-     :ft [:ft (tuc/draw-normal 152 17)]
-     :m [:m ((convert-units-f :ft :m) (nth (typical-stage-length :ft)))])))
+     :ft [(tuc/draw-normal 152 17) :ft]
+     :m [((convert-units-f :ft :m) (nth (typical-stage-length :ft) 0)) :m])))
 
 (defn typical-stage-extent
   ([]

                   [:kPa :psi] #(/ % (factors [:psi :kPa]))
                   [:kPa :MPa] #(/ % (factors [:M :k]))
                   [:MPa :kPa] #(* % (factors [:M :k]))
                   [:C :F] #(+ (* % 1.8) 32)}]
    (converter [from to])))


        (keyword? arg)
        (repeatedly (fn [] (typical-surface-treating-pressure arg)))))

(defn typical-slurry-rate
  ([]
   (let [unit (rand-slurry-rate-unit)]
     (typical-slurry-rate unit)))
  ([unit]
   (let [typical-value (cond (or (= unit :bbl-per-min)
                                 (= unit :bpm))
                             (value-from-typical-range 75 100)
                             (or (= unit :m3-per-min)
                                 (= unit :m3/min))
                             (value-from-typical-range 11.92 15.9))]
     [typical-value unit])))

(defn slurry-rate-seq [arg]
  (cond (int? arg)
        (let [unit (rand-slurry-rate-unit)]
          [unit (take arg (slurry-rate-seq unit))])
        (keyword? arg)
        (repeatedly (fn [] (typical-slurry-rate arg)))))

(defn typical-proppant-concentration
  ([]
   (let [unit (rand-proppant-concentration-unit)]
     (typical-proppant-concentration unit)))
  ([unit]
   (let [typical-value (cond (or (= unit :lb-per-gal)
                                 (= unit :lb/gal))
                             (value-from-typical-range 0.2 10)
                             (or (= unit :kg-per-m3)
                                 (= unit :kg/m3))
                             (let [conversion (/ 0.453592 0.00378541)]
                                (value-from-typical-range (* 0.2 conversion) (* 10 conversion))))]
     [typical-value unit])))AbstractMethodError

(defn proppant-concentration-seq [arg]
  (cond (int? arg)
